In this proposal we plan to continue our investigations into the functions of steroid hormones on neural differentiation. Although we know from physiological studies that prenatal testosterone can androgenize the central nervous system (CNS) of female monkeys, little is known of how this is accomplished. Previously, we determined the concentrations of several potent steroids in the blood stream of the fetal rhesus monkey. We now plan to compare these levels by radioimmunoassay with the quantities found in the fetal brain at various times in gestation and to investigate the action of progesterone (P) on the regulation of these levels. Enzymatic activities such as the E2-dehydrogenase and the 5a reductase may control levels of steroids in adult reproductive tissue. Can P act similarly in nervous tissue of the embryonic monkey? We postulate that P is important to sexual differentiation because of its antiandrogenic properties. We would like to know what antiandrogenic means with regard to P action. Other aspects of biological regulation such as the ontogeny of cyclic AMP in neural and gonadal tissues, the effects of dibutyryl cyclic AMP and gonadotropins on fetal gonadal steroidogenensis, and the correlation of these functions will be investigated. Finally, the residual cyclic mechanism for the release of gonadotropins contained in the CNS and (or) pituitary of the male monkey will be investigated.